The present invention relates to a method and apparatus for continuously forming a uniform layer of material that is being dispersed.
German Offenlegungsschrift 34 04 658 dated Aug. 14, 1985 belonging to the assignee of the present invention, and applicant's copending U.S. patent application Ser. No. 791,225, filed Oct. 25, 1985 also belonging to the assignee of the present invention, disclose feeding the individual components of a material that is to be dispersed to a continuous mixer in a volumetrically and/or weight-metered manner. The mixed material is constantly withdrawn from the mixer as a material stream. Before this stream of material that is to be dispersed is delivered to a dispersal mechanism for uniform deposition as a dispersed material layer (mat) upon a continuously rotating molding belt for the manufacture of sheets, this material stream is discharged to an intermediate hopper for homogenization purposes. From this hopper, the material that is to be dispersed is withdrawn via a conveyer belt that is preferably regulated in conformity with the material stream, with one or more equalizing rollers being disposed on this conveyer belt. These equalizing rollers push or comb the overhanging material of the stream back counter to the direction of travel of the conveyer belt. The material stream, the cross-sectional area of which is regulated in this manner, is supplied to the dispersal mechanism.
The continuous formation of uniform layers of dispersed material pursuant to the previously described known methods has proven to be expedient for wood chipboards, mineral fiber sheets, and also for wood cement boards, gypsum chip boards, and gypsum fiber boards. However, where compressible material that is to be dispersed is involved, the homogenization of the material stream via an intermediate hopper is satisfactory only if, at a constant withdrawal cross section, the height of the material in the intermediate hopper is also to a large extent kept constant.
However, even under circumstances involving for the most part uniform withdrawal of material that is to be dispersed from an intermediate hopper, where the material has wider particle sizes, undesired classifying or separating effects occur as a result of the equalizing rollers that brush back the material that is to be dispersed.
In addition, the homogenization of a material stream via an intermediate hopper is extremely problematic for material that is to be dispersed and that contains rapidly hardening binding agents, such as moist, accelerated gypsum. However, it is precisely this rapid reaction of the gypsum that is advantageous for a continuous, rapid manufacturing process without long maturing times for the end products (sheets). In so doing, the easy formability of material mixtures containing gypsum is assured only if the binding process has not yet begun during the forming or compaction process. However, this extremely strict and time-critical criterium requires a precise and predeterminable processing time for the material from the time it is moistened until the compaction following the dispersal mechanism. However, with a material that is to be dispersed and that is temporarily stored in an intermediate hopper, and which in addition is homogenized via equalizing rollers that brush the material back, the retention time of at least a portion of the material is uncertain. It is not possible to preclude material particles from circulating in the intermediate hopper, as a result of being brushed back by the equalizing rollers, until they are bound.
It is therefore an object of the present invention to provide a method and apparatus for continuously forming a uniform layer of material that is being dispersed whereby all of the particles or components of the material are supplied for processing at the same speed without having a classifying effect occur.